feat(testing): add resilience state probes

[thomhurst]

Closes #100

Adds immutable v1 state snapshots for circuit breakers, rate limiters, and concurrency limiters, plus typed/untyped ExecutionProbe wrappers for deterministic attempt and cancellation assertions. Snapshot reads reuse existing state atomics and locks; production execution paths gain no probe hooks or extra work.

Validation:

• dotnet build Kevlar.slnx -c Release
• Kevlar.Tests: 670 passed
• Kevlar.Testing.Tests: 21 passed
• Kevlar.IntegrationTests: 34 passed
• Kevlar.Analyzers.Tests: 38 passed
• Kevlar.Chaos.Tests: 23 passed
• Kevlar.AllocationTests: 2 passed
• dotnet pack + Verify-Packages.ps1 passed
• Verify-DocSnippets.ps1: 97 snippets passed
• docs npm run build passed

Summary by CodeRabbit

• New Features

  • Added immutable state snapshots for shields, circuit breakers, rate limits, and concurrency limits.
  • Added execution probes to track attempts and cancellation requests, with asynchronous wait support.
  • Added snapshot support for typed and untyped shields, including strategy ordering and contract versions.

• Documentation

  • Added guidance and examples for inspecting resilience state during live testing.

• Tests

  • Added coverage for limiter queues, circuit states, retries, cancellations, shared state, and fake-time behavior.

[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between 7bd6799 and c235e5a.

📒 Files selected for processing (1)

• tests/Kevlar.Testing.Tests/TelemetryRecorderTests.cs

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📝 Walkthrough

Walkthrough

The change adds immutable, versioned resilience-state snapshots for shields and limiter strategies. It also adds ExecutionProbe for attempt and cancellation tracking, asynchronous wait helpers, internal state capture, tests, public API entries, and documentation.

Changes

Resilience state snapshots

Layer / File(s)	Summary
Versioned shield state snapshots src/Kevlar.Testing/*StateSnapshot.cs, src/Kevlar.Testing/ShieldStateSnapshotExtensions.cs, src/Kevlar/Strategies/...	The testing assembly defines immutable snapshots for shield strategies. Extensions capture indexed circuit-breaker, rate-limit, and concurrency-limit state. Internal strategy methods expose the required metrics.
Execution attempt and cancellation probing src/Kevlar.Testing/ExecutionProbe.cs, src/Kevlar.Testing/ExecutionProbeSnapshot.cs	ExecutionProbe wraps typed and untyped asynchronous delegates, counts attempts and cancellations atomically, forwards cancellation tokens, and supports threshold wait methods.
Contracts, validation, and documentation src/Kevlar.Testing/PublicAPI.Unshipped.txt, tests/Kevlar.Testing.Tests/StateProbeTests.cs, tests/Kevlar.Testing.Tests/TelemetryRecorderTests.cs, docs/docs/testing.md	Public API entries, state-sharing and fake-time tests, typed-shield tests, cancellation tests, null validation, test isolation, and testing documentation cover the new contracts.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Merge Risk: ⚪ Minimal · up to c235e

The PR adds testing probes and immutable state snapshots with no production execution-path overhead; no actionable merge-blocking risk remains after normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant Shield
  participant SnapshotExtensions
  participant Strategies
  Shield->>SnapshotExtensions: GetStateSnapshot()
  SnapshotExtensions->>Strategies: Capture state
  Strategies-->>SnapshotExtensions: Return strategy metrics
  SnapshotExtensions-->>Shield: Return immutable snapshot

Loading

Poem

I hop through snapshots, tidy and bright,
Counting each attempt through the night.
Cancellations ring, permits align,
Fake clocks make rate limits shine.
Safe probes bloom in testing’s burrow.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 18.92% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 37 functions across 12 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the primary change: adding resilience state probes for testing.
Linked Issues check	✅ Passed	The changes add versioned snapshots, typed and untyped execution probes, API declarations, documentation, and focused tests for the linked requirements [#100].
Out of Scope Changes check	✅ Passed	The changes are focused on resilience snapshots, execution probes, related APIs, documentation, and test reliability.

✨ Finishing Touches 💡 1

📝 Generate docstrings 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch issue-100-state-probes

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